Previous studies show the classical approach of using only negative feedback in controlling dynamic and steady-state performance of control systems. See, for example, N. K. Sinha, "Control Systems", Holt, Rinehart and Winston, 1986, pp. 59-70, G. H. Hostetter et al, "Design of Feedback Control Systems", Holt, Rinehart and Winston, 1982, pp. 3-5, B. C. Kuo, "Automatic Control Systems", Prentice-Hall, Inc., 4th Ed., 1982, pp. 3-16.
In the field of switch-mode power converters, this classical approach is maintained as seen from K. K. Sum, "Switch Mode Power Conversion", Marcel Dekker, Inc., 1984, pp. 2-4, G. Chryssis, "High-Frequency Switching Power Supplies", McGraw Hill, 1984, pp. 133-148, 173-194, P. R. K. Chetty, "Switch-Mode Power Supply Design", TPR 1986, pp. 48-60, 60-68, 69-81.
R. Redl and N. O. Sokal, "Near-Optimum Dynamic Regulation of DC-DC Converters Using Feed-Forward of Output Current and Input Voltage with Current-Mode Control", IEEE Transactions on Power Electronics, VOL.PE-1, No. 3, July 1986, pp. 181-192, proposed near-optimum dynamic regulation of a dc-to-dc converter by adding feed-forward of output current and input voltage to a current-mode converter. However, Redl and Sokal did not disclose any algorithm to obtain complete load invariance.
J. H. Murdock discloses a current-mode control arrangement with load dependent ramp signal added to sensed current waveform in the U.S. Pat. No. 4,672,518. The reader may also find of interest the U.S. Pat. Nos. 4,293,812 of H. Kubach et al, 4,578,631 of S. Smith, and 4,686,617 of R. M. Colton, and 4,456,872 of T. A. Froeschle, the German Pat. Nos. 2625036 and 2823437, the Japan Pat. Nos. 219966 and 10816, the U.S.S.R Pat. No. 949647, as well as the references: G. A. Rudy, "Constant-Voltage Switching Regulator", IBM Technical Disclosure Bulletin, Vol. 14, No. 9, pp. 2784,5, Feb. 1972, and R. C. Yeager, "Skipping Chopper Cycles in Switching Regulator", IBM Technical Disclosure Bulletin, Vol. 18, No. 11, pp. 3737,8, April 1976. None of these patents and references, however, discloses any possible use of positive current feedback and with that in connection an algorithm to obtain complete load invariance.